As a building unit which constitutes a unit building, there have conventionally been box-shaped framing structure having four columns, four floor beams and four ceiling beams as structural framing members (structural members forming the framing sharing horizontal and vertical forces)(Prior art A).
Another conventional building unit is proposed in Japanese Patent Application Laid-Open (JP-A) No. 57-201441, which has columns set on floor structure with no ceiling (Prior art B).
However, these conventional arts have problems as described below.
(Prior art A)
Ceiling height RH cannot be secured large. That is, as shown in FIG. 9, the transportation height limit Hx for transporting the factory manufactured building units to construction sites is fixed (3800 mm according to the present traffic regulations). Having the height of truck loading floor at the technically lowest limit, the maximum value for the unit height UH is 2940 mm, for example. When span L is desired to be about 6.3 m for the building unit of a two story house, the rational depth dimensions B.sub.1 and B.sub.2 for floor beams and ceiling beams which are constructed with steel members of limited thickness are approximately 240 mm. Taking the dimension above beam b.sub.1 and the dimension below beam b.sub.2 at 30 mm and 60 mm, respectively, the ceiling height RH is UH-(B.sub.1 +b.sub.1 +B.sub.2 +b.sub.2)=2370 mm as the limit.
(Prior art B)
(1) Since a building unit is not provided with ceiling beams, ceiling cannot be provided at the factory manufacturing stage, and building interior structure such as partitions cannot be completed. Therefore, the factory manufacturing efficiency cannot be improved (FIG. 8(A)).
(2) When a building unit is stored at store yard, the cover sheet which is provided around the building unit droops down due to the rain water deposited on top thereof (FIG. 8(B)).
(3) When a building unit is hoisted up for such as installation, there is a risk that the whole shape can be deformed (FIG. 8(C)).
In order to avoid the problem described in above (2), it is necessary to temporarily provide support members in-between the upper end portions of columns of the building units, as disclosed in Japanese Patent Application Publication (JP-B) No. 3-30659.